The present invention relates generally to fireplace furnaces adapted for insertion within existing conventional fireplaces.
Conventional fireplaces are notoriously inefficient room heaters because they draw warm air into the fireplace and up the chimney when used. This problem can be solved by use of doors on the fireplace, but their use substantially reduces the radiation of heat from a fire in the fireplace into the room.
To improve the efficiency of such fireplaces, several approaches have been taken. Fireplace furnaces of the "heat-alator" type are well known, in which the fireplace itself is built with special heat outlet openings in the front wall of the fireplace above or alongside the fireplace opening so that air can be circulated along side and rear heat exchanging surfaces of the firebox and heated for discharge into the room through such openings. However, these designs all require either rebuilding or modification of an existing fireplace or installation of the furnace during the original construction of the fireplace.
To provide a more efficient fireplace furnace, I designed a self-contained prefabricated fireplace furnace for insertion within a conventional fireplace, shown in my U.S. Pat. No. 4,015,581, issued Apr. 5, 1977. The heater unit includes a metal firebox within a surrounding metal jacket. Room air is drawn into side inlet openings at the front of the jacket, warmed by the firebox walls serving as heat exchange surfaces, and then expelled back into the room through an upper portion of the jacket, all by natural convection. Although this heater is satisfactory to maintain warm temperatures in a room, it requires a considerable length of time to heat a cold room because of the low rate of air movement through the heater.
Use of fans to provide forced air circulation through fireplace heaters has been proposed in U.S. Pat. Nos. 2,642,859 and 2,743,720. However, use of such fans does not entirely solve the problem because of their tendency to move air through the heater and back into the room before the air can be adequately warmed by the limited heat exchange surfaces of the heater.
I therefore advised a further improved fireplace furnace as disclosed in my application for patent, Ser. No. 843,986, filed Oct. 20, 1977, now U.S. Pat. No. 4,166,444. Such furnace has a jacketed firebox with heat exchange tubes extending through the firebox from the airspace at the rear of the firebox to discharge openings at the front of the firebox. This design enables efficient use of the heat produced by a fire by circulating room air, first through the side and rear airspaces and then through the heat exchange tubes, thereby exposing such air to progressively hotter portions of the firebox chamber.
As a further development of the foregoing design, I devised a combination fireplace furnace and cookstove as disclosed in my application for patent, Ser. No. 973,875, filed Dec. 28, 1978. This design includes a cookstove portion which protrudes into the room from the firebox when the firebox is positioned in the fireplace. Such portion can be used for cooking and increases the effectiveness of the furnace because of its ability to radiate heat from the exposed surfaces of the cookstove portion into the room as well as circulate warm room air.
In the use of conventional wood stoves it is common practice to bank the coals of a fire at night and to reduce the draft to slow their burning, so that the fire can be easily restarted from the glowing coals in the morning. It would also be desirable to be able to bank a fire in the fireplace furnaces of my foregoing patents and applications. However, banking has not proven feasible because of the proximity of the blowers to the hot side walls of the firebox. The electric motors of such blowers can be damaged by the extreme heat of the banked coals particularly when the blowers are turned off.
Therefore, a primary object of the present invention is to provide a fireplace furnace having all of the advantages of my prior fireplace furnaces and, in addition, the ability to safely and effectively bank the coals of a fire when desired without damaging the blowers.
Another primary object of the invention is to increase the heating effectiveness of my fireplace furnaces.
A specific object of the invention is to further enhance the ability of my fireplace furnaces to progressively heat ambient room air through improved air circulation within the furnace airspaces and improved firebox baffling.